In hydrocarbon exploration operations, well boreholes are drilled by rotating a drill bit attached to a drillstring, and may be bored vertically or bored in selected directions via geosteering operations. Various downhole devices located in a bottomhole assembly (BHA) or other locations along the drillstring measure operating parameters, formation characteristics, and include sensors for determining the presence of hydrocarbons.
One type of device used to measure downhole properties is a nuclear magnetic resonance (NMR) device. An NMR device creates a magnetic field that excites nuclei and causes them to precess around the direction of the magnetic field. The energy related to the moving nuclei can be measured and information about a sample of interest (e.g. a fluid in a formation or wellbore) may be ascertained.
Porosity and the other NMR answer products (e.g., fluid volumetrics, permeability, saturation, viscosity, fluid typing, pore size distribution) are affected by axial and lateral motion (or lateral vibrations) of the NMR tool and by the uncertainty related to the hydrogen index (HI) correction. One approach to reduce the axial movement affects is to reduce the rate of penetration (ROP) of the drillstring and, consequently, NMR device.